Chemically specific subpopulations of neurons in the cat retinal will be identified through the use of neurotransmitter substances as cytochemical markers in light and electron microscopic studies. Distinctive morphological features and synaptic relationships of each subpopulation will be described. Autoradiographic techniques will be used to study subpopulations which accumulate glycine, GABA, and taurine. Retinal neurons characterized by neuroactive peptides including substance P, somatostatin, and enkephalin will be identified by the use of both autoradiographic and immunocytochemical techniques. The electron dense marker, 5,6-dihydroxytryptamine, will be used to identify neurons which employ dopamine and indoleamine as transmitters. Functional pathways will be studied through autoradiographic analysis of neurotransmitter and 2-deoxyglucose uptake under controlled stimulus conditions. The effects of light vs. dark, rod vs. cone stimulation, and varying wavelengths of light will be investigated. The anatomical relationships between chemically defined subpopulations will be explored through the use of double labeling studies in which autoradiography will be combined with Golgi impregnation, immunocytochemistry and retrograde transport. The identification of morphologically distinct subpopulations of retinal neurons which utilize specific chemical transmitters and the definition of stimulus conditions which influence the release of these transmitters will provide a basis for integration of anatomical, neurochemical, and physiological data. Elucidation of structural and chemical circuitry in the cat retina will furnish basis information regarding the initial processing of visual information in a mammalian retina.